#!/bin/sh

# when $3 is empty, template is read from working directory
template="$1" base_rev="$2" tip_rev="$3"
status=0

die() {
	printf '%s\n' "$*" >&2
	exit 1
}

if ! [ "$base_rev" ]; then
	die "usage: $0 TEMPLATE BASE-REVISION [TIP-REVISION]"
fi

if ! command -v git >/dev/null 2>&1; then
	die "neither chroot-git nor git could be found"
fi

scan() {
	rx="$1" msg="$2"
	template_path=$template
	maybe_git=
	if [ "$tip_rev" ]; then
		template_path="${tip_rev}:${template}"
		maybe_git="git"
		revspec="[^:]*:"
	fi
	$maybe_git grep -P -Hn -e "$rx" "$template_path" |
		grep -v -P -e "[^:]*:[^:]*:\s*#" |
		sed "s/^${revspec}\([^:]*:[^:]*:\)\(.*\)/\1 $msg/"
}

show_template() {
	rev="$1"
	if [ "$rev" ]; then
		git cat-file blob "${rev}:${template}" 2>/dev/null
	else
		cat "${template}" 2>/dev/null
	fi
}

show_template_var() {
	rev="$1" var="$2"
	(
		show_template "$rev"
		printf '%s\n' "printf '%s\\n' \"\$${var}\""
	) | bash 2>/dev/null
}

revision_reset() {
	[ "${revision}" = 1 ] && return
	if [ "$prev_version" ]; then
		case "$prev_reverts" in
			*"$version"_*) return
		esac
		action=update
	else
		action=creation
	fi
	scan "^revision=" "revision should be set to 1 on ${action}"
	status=1
}

reverts_on_downgrade() {
	[ "$version" ] || return
	case "$reverts" in
		*"$prev_version"_*) ;;
		*)
			scan "^version=" "missing reverts= for downgrade $prev_version to $version"
			status=1
	esac
}

check_revert() {
	for vr in $reverts; do
		xbps-uhelper cmpver "${version}" "${vr%_*}"
		case "$?" in
		0 | 1)
			scan '^version=' "remove $vr from \$reverts"
			status=1
			;;
		esac
	done
	for vr in $prev_reverts; do
		if ! xbps-uhelper cmpver "$version" "${vr%_*}"; then
			continue
		fi
		if [ $revision -gt "${vr##*_}" ]; then
			continue
		fi
		scan '^revision=' "undo a revert with same revision as before"
		status=1
	done
}

version_change() {
	version="$(show_template_var "$tip_rev" version)"
	revision="$(show_template_var "$tip_rev" revision)"
	reverts="$(show_template_var "$tip_rev" reverts)"
	prev_version="$(show_template_var "$base_rev" version)"
	prev_reverts="$(show_template_var "$base_rev" reverts)"
	xbps-uhelper cmpver "$version" "$prev_version"
	case "$?" in
		1) revision_reset;;
		-1|255) reverts_on_downgrade;;
	esac
	check_revert
}

version_change

exit $status